Mysterious night-time pulsing sound

Over the last few months, I’ve occasionally heard a strange sound coming in through my open window at night. It’s a distant electronic pulsing sound which comes and goes on the wind. It seems to be coming from the north of Edinburgh around Leith. It’s quiet, but distinct. I decided to record it. The resulting recording is a bit shoddy, but it does the job.

Leith Night Pulse

I’ve no real idea what could be making this sound. Any suggestions would be welcome. It sounds to me like an alarm or an alert, like it has been designed to sound as it does. I tend to hear it around 1-3 am. Given the direction it’s coming from, it could be something happening on Leith docks or something going on at the nearby sewage works. It might even be something happening on the large cargo ships and oil tankers which often sit out in the Firth of Forth. I live maybe a mile from the coast; the way it drifts on the wind suggests that the sound source is quite far off.

Some technical details about the recording

This was a bit of a hard one because the pulsing sound was very quiet and I wanted to document it to make it clearly audible. So the approach I took was to focus on and magnify the pulsing sound at the expense of an accurate recording of the general ambience.

As it was so late at night, the ambient sound level was pretty low anyway. To get a decent level, I had to turn up the gain on my Sound Devices 702 to maximum. To reduce the effect of noise from my flat and the building, I stuck the mic (my Rode NT4 in a Rycote full modular windshield) out of the kitchen window on a fully-extended mic stand. A boom pole would have been better but I didn’t have one. I turned off the freezer in the kitchen as with the gain so high the mic was picking up a lot of the hum from that. The hum was probably louder than the pulsing sound itself. I tried to stay completely still – with the gain so high, even the tiniest sounds could be picked up. Even though I was careful, there are lots of extraneous noises in there. Little floorboard creaks, doors closing elsewhere in the building.

Annoyingly, after a few minutes the battery on my 702 died and I had neither my spare battery nor the power supply to hand. I switched to a Tascam DR100 recorder, but the preamps on that aren’t as good.

Afterwards, working with the SD702 recording, it was very quiet so I normalised it. This made the pulse louder but of course also brought up the level of all the stuff I didn’t want as well, like bass rumble and hiss. So I then did some pretty strong EQ work to remove noise at the low and high ends of the frequency spectrum. I also slightly boosted the main frequency of the pulse to bring it out of the mix a bit more. The process was very rough and ready and not at all audiophile really, but it got the result I wanted: the pulse is now clearly audible, whereas insitu it was very quiet, only just detectable over the background noise.

If this sound keeps happening, I might try a few more recordings on still nights, hopefully with a bit more care and preparation..

20 Replies to “Mysterious night-time pulsing sound”

  1. I can’t play your link unfortunately but I’m in Coventry and can hear a bleeping like a submarine off of James Bond films back in the day. It seemed sporadic but it’s still repeating 10 minutes after I heard it through my open window. Weird!

  2. I heard this pulsating sound last night around 2:30am. It wasn’t constant and appeared to become louder and then quieter.

  3. Same here, Edinburgh , Craighouse Gardens. 3am the sound is driving everyone mad, it can be heard for over 2 weeks now every night going louder and quieter, it’s like that ringing in the ears that won’t stop… what is it people???

  4. Ive got the same description of sound as kay above. Like a submarine radar pulsing in an old james bond film. It seems to get more loud at night possibly because of less activity and environment noise around This is driving me insane its like the drip of a chinese water torture

  5. I lived in Reading for one year and now live near Woking – in Reading I heard a low, deep pulse almost every single night. I have just started to hear the same thing now near Woking. I cannot pick it up on a recording and can almost ‘feel’ it as much as hear it. It’s odd to describe. It’s prevents me from sleeping and usually starts around midnight and lasts until roughly 6am.

  6. I was just watching videos on YouTube and it is 8:55 PM in South Carolina and opposing noise just came from outside and I can hear the walls. Sounded like my heads going to explode it was so intense !

  7. I heard this strange pulsating sound last night in Pasadena California around 1:45am. Woke me up from my sleep seemed to get closer and fade away. It was almost as if you could feel the pulses in your body. Honest to God scariest thing I ever heard. Strange also there were airplanes that seemed to follow at top speeds after but nothing I have ever heard before. The pulsing itself lasted about 10 minutes to completely move over from sounding far to almost on top of the house although that what it felt like. I couldn’t see anything at all I just could hear this strong pulsing sound… also the chickens in my neighbors house were losing their minds.. really scary..wonder what it was.

  8. I live on hill in Pt Ludlow Wa. For the three years we have been living here, at night from about 2 a.m. to around 6 a.m.- this varies some, and I don’t always sleep downstairs- I hear a very low pulsating vibrating sound which is very bothersome. What to think? Unrelated, which happened about ten years ago when my husband and I backpacked to a high remote area about ten miles above Pt. Angeles WA. Went on and on during the evening and night deep underground pulsing…like a machine motor. Husband is a deep sleeper- no problem for him.

  9. Thanks for your comment. I really don’t know – but I will say you’re not alone. What you are describing is usually referred to as ‘the hum’. Since writing briefly about these mysterious sounds many years ago, every now and then I get comments submitted by people who claim to be hearing similar sounds. Andy Moorhouse at Salford did some research on this years ago – his reports on the matter can probably be found online and might be worth a read.

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